A variety of drilling apparatuses are known for the formation of holes in structural steel shapes, e.g. the webs of the above mentioned beams, and can comprise a drilling or boring head disposed on a support which can be provided with a roll conveyor or like transporter for the structural steel shape or workpiece. Various degrees of mobility are provided for the head to enable the drill bit to be positioned at a proper location for drilling.
Reference may be had to the following U.S. Patents directed to drilling or related apparatuses for structural steel shapes and the like:
U.S. Pat. No. 4,676,000 issued 30 June 1987; U.S. Pat. No. 4,691,601 issued 8 Sept. 1987 and U.S. Pat. No. 4,632,365 issued 30 Dec. 1986. Reference may also be had to the following U.S. Applications directed to drilling apparatuses and the like: Ser. No. 07/303,603 filed 17 Jan. 1989; Ser. No. 07/316,754 filed 28 Feb. 1989; Ser. No. 07/316,756 filed 28 Feb. 1989; Ser. No. 07/316,757 filed 28 Feb. 1989; and Ser. No. 07/274,056 filed 29 Sept. 1988.
It is known, in connection with such apparatuses to mount the tool carrier, namely the drill bit holder and a motor for rotating the carrier and the drill bit, on the drilling head with aid of a drilling-feed piston and cylinder arrangement which can be controlled by fluid means and to utilize as control elements a proximity or position switch to output a control signal.
The control device can permit the drilling apparatus to be integrated in a line for the automatic processing of structural steel shapes. The control device can effect an advance or feed of the tool carrier with the tool and an extraction movement of the latter generally to a rest position which corresponds to the original starting position of the tool or carrier.
However, as far as I am aware, there has been no simple system provided heretofore which would permit automatic retraction of the drill bit to a position different from its starting position or located between its position of engagement with the workpiece and the original starting position, into a rest position preparatory for the drilling of the next hole. Stated more precisely, I am not aware of any simple arrangement which will allow retraction of the drill bit so that its tip or point is located at a predetermined distance from the surface of the workpiece preparatory for the next drilling operation and independent of the fully retracted or original starting position of the drill bit.
This positioning of the tool is important because it permits more rapid onset of the next drilling operation by eliminating the need to displace the drill bit excessively in both the retraction and the tool advance strokes.